The present invention relates to a fibrous aggregate formed by processing fibrous material comprising fibers in particular, a fibrous aggregate which is relatively low in density and is relatively thick. It also relates to a thermal method for forming such a fibrous aggregate, and an apparatus for forming such a fibrous aggregate.
Conventional methods for forming a fibrous aggregate, which are widely in use, may generally be classified into two groups: the needle punching group and the thermal group. In certain cases, a needle punching method and a thermal method are independently used, whereas in other cases, they are used in combination.
Next, the two groups of fibrous aggregate forming methods will be briefly described.
(1) Needle Punching Method
This is a method for continuously forming a sheet of fibrous aggregate by entangling fibers among themselves; multilayered fibrous material is reciprocally punched through with the use of a needle punching machine which uses a needle called a felting needle.
(2) Thermal Method
This is a method for forming a fibrous aggregate by thermally welding fibers among themselves; a predetermined amount of heat is applied to multilayered fibrous material comprising plural types of fibers different in melting point, so that the fibers with the lower melting point (bonding material) melt and weld the fibers with the higher melting point (structural material), at the intersections of the fibers with the higher melting point. In other words, according to a thermal method, the fibers with the higher melting point serve as structural material, whereas fibers with the lower melting point serve as bonding agent. As for typical thermal methods, there are a method called a heated air conveyer heating chamber method, in which multilayered fibrous material is continuously fed into a heated air conveyer heating chamber to form a continuous form of fibrous aggregate, a method called a molding method, or a batch method, in which multilayered fibrous material is packed into a mold of a predetermined size and is heated to form a block form of fibrous aggregate, which has a predetermined size (size and shape).
Next, the two methods will be described in more detail.
(2-a) Heated Air Conveyer heating chamber Method
FIG. 12 is a schematic sectional view of a conventional heated air conveyer heating chamber used for a thermal fibrous aggregate forming method. As is evident from FIG. 12, this heated air conveyer heating chamber 500 has a pair of mesh belts 510 and 520, which are placed in a manner to vertically oppose each other, with the provision of a predetermined gap between the two belts, in order to move the multilayered fibrous material 600, in the leftward direction of the drawing, while compressing the multilayered fibrous material 600 from the top and bottom sides (in the direction in which the fibers are stacked), as the multilayered fibrous material 600 is fed from the upper right direction of the drawing. The multilayered fibrous material 600 is actually layers of webs of sheathed fiber. Each web has been produced with the use of a carding machine (unillustrated), a cross-laying machine (unillustrated), or the like, and the fibers in each web have been laid more or less in parallel. The weight per unit of area of the multilayered fibrous material 600 is selected in accordance with its usage. Further, the multilayered fibrous material 600 comprises plural types of fibers different in melting points.
The distance between the two mesh belts 510 and 520 is approximately equal to the thickness of the final product, or a continuous fibrous aggregate 650, and can be adjusted as necessary. The thickness H of the continuous multilayered fibrous material 600 fed into the heated air conveyer heating chamber 500 is greater that the gap h between the two mesh belts 510 and 520. After being fed into the heated air conveyer heating chamber 500, the continuous multilayered fibrous material 600 is compressed all at once to the thickness h by the mesh belt 510 and 520, and is thermally formed into the continuous fibrous aggregate 650 while remaining in the compressed state.
In order to thermally form the continuous multilayered fibrous material 600 into a continuous fibrous aggregate 650, an air sending chamber 530 for blowing air, and an air receiving chamber 540 for suctioning the heated air blown out of the air sending chamber 530, are provided in the heated air conveyer heating chamber 500. The air sending chamber 530 is provided with an air supplying hole 531 and a plurality of perforations, and is located above the path of the multilayered fibrous material 600, within the heated air conveyer heating chamber 500. Heated air is blown into the air sending chamber 530 through the air supplying hole 531, and is blown out of the air sending chamber 530 through the plurality of perforations 532 to be blown at the multilayered fibrous material 600. The air receiving chamber 540 is located below the path of the multilayered fibrous material 600, and is provided with a plurality of perforations 542 and a plurality of air suctioning holes 541. As the heated air having been blown at the multilayered fibrous material 600 from the air sending chamber 530, as described above, passes through the multilayered fibrous material 600, the heated air is suctioned into the air receiving chamber 540 through the plurality of perforations 542, and is exhausted through the plurality of air suctioning holes 541.
Upon being introduced into the heated air conveyer heating chamber 500, the continuous multilayered fibrous material 600 is heated by the heated air blown out of the air sending chamber 530 until its temperature rises to a predetermined one. As described above, the continuous multilayered fibrous material 600 is continuous layers of plural types of fibers different in melting point. Therefore, the fibers, which have a relatively lower melting point, can be melted by setting the temperature of the heated air to a temperature which is higher than the melting point of the fibers with a relatively lower melting point, and is lower than the melting point of the fibers with a relatively higher melting point, so that the fibers with the relatively higher melting point, can be bonded among each other at their intersections, with the melted fibers with the lower melting point acting as bonding agent, to effect a continuous fibrous aggregate 650, which has a predetermined thickness.
(2-b) Mold Based Method
FIG. 13 is a drawing for depicting one of conventional methods for forming a fibrous aggregate. A block of multilayered fibrous material 610 is identical in material to the continuous multilayered fibrous material 600 used in the heated air conveyer heating chamber based method, except that it is in the form of a block. More specifically, as shown in FIG. 13(a), the multilayered fibrous material block 610 comprises several layers of fibers, in which fibers are aligned approximately in parallel in a certain direction a, and which are stacked in a direction b perpendicular to the direction in which the fibers are aligned in each layer. This multilayered fibrous material block 610 is placed in an aluminum mold 700, and is covered with a lid 710 as shown in FIGS. 13(b) and (c). At this stage, the multilayered fibrous material block 610 in the mold 700 has been simply compressed in the stacking direction b, in the mold 700. Then, a block of fibrous aggregate is obtained by heating the mold 700 until the aforementioned condition is satisfied.
However, the above described methods for forming a fibrous aggregate block have such problems of their own that will be described below.
(1) Needle Punching Method
A needle punching method physically causes fibers to entangle, with the use of a felting needle. Therefore, a fibrous aggregate produced by a needle punching method is hard, thin, and high in bulk density. In other words, a soft and thick fibrous aggregate which is low in bulk density is difficult to produce using a needle punching method.
(2a) Heated Air Conveyer heating chamber Based Method
In a heated air conveyer heating chamber based method, heated air is blown at multilayered fibrous material from above, and therefore, the fibers in the layers on the top side tend to soften before those in the layers on the bottom side. As a result, the layers on the top side tend to be collapsed by the pressure from the heated air from above, and also the self-weight of the layers of fibers, causing the layers on the top side to become higher in bulk density than the layers on the bottom side. In other words, it is difficult to produce a fibrous aggregate uniform in density using a heated air conveyer heating chamber based method. One of the solutions to this problem is to reduce the velocity of the heated air. However, reducing the heat air velocity makes it impossible for the heated air to pass through the multilayered fibrous material, creating a problem in that it is virtually impossible to heat the bottom portion of the multilayered fibrous material.
Therefore, producing a soft and thick fibrous aggregate which is low and uniform in bulk density using a heated air conveyer heating chamber based method is as difficult as producing it using a needle punching method, admitting that a relatively hard sheet of fibrous aggregate which is relatively high in bulk density can be as easily produced by the latter method as the former method. In addition, the layered fibrous material is heated while being kept in the compressed state by the mesh conveyer, and therefore, there is a problem in that the pattern (ridges and recesses) of the mesh conveyer is imprinted onto the surface layer of the multilayered fibrous material.
(2b) Mold Based Method
Referring to FIG. 14, the problems associated with methods for forming a fibrous aggregate using a mold will be described. FIG. 14 is a drawing for depicting the state of the inside of a mold during the production of a fibrous aggregate using a mold.
As the mold 700 begins to be heated after the multilayered fibrous material block 610 is packed into the mold 700 and the mold 700 is sealed with the lid 710, the multilayered fibrous material block 610 begins to gradually collapse in the gravity direction starting from its fringe. This phenomenon is not conspicuous when the plural types of fibers in the multilayered fibrous material block 610 are very different in melting point, for example, when one group of of fibers in the multilayered fibrous material block 610 is formed of polyethylene, and the other group of fibers is formed of polypropylene-terephthalate. However, if the two groups of fibers are selected from among olefinic materials alone, the phenomenon becomes very conspicuous. This may be due to the fact that in this case, there is little difference in melting point between the two groups of fibers, and therefore, the effects of the heat transmitted from the mold 700 first manifest in the fringe portions of the multilayered fibrous material block 610.
As the heating of the mold 700 is continued, heat is conducted all the way to the center of the multilayered fibrous material block 610, causing the entirety of the adjacencies of the bottom surface of the multilayered fibrous material block 610 to collapse as shown in FIG. 14(b). When the multilayered fibrous material block 610 is in this state, the bulk density of the multilayered fibrous material block 610 is nonuniform in terms of the gravity direction; the top portion of the multilayered fibrous material block 610 is lower in bulk density than the bottom portion of the multilayered fibrous material block 610 because the bottom side of the multilayered fibrous material block 610 is more affected by the weight of the multilayered fibrous material block 610 itself. In other words, a high bulk density region 610a and a low bulk density region 610b coexist in the multilayered fibrous material block 610; an undesirable bulk density gradient has been created.
As described before, in the case of a conventional mold based method, bulk density gradient occurs, and therefore, a fibrous aggregate block which is relatively high in hardness and bulk density, such as the one formable by a conventional heated air conveyer heating chamber based method, can be easily formed, but a soft and thick fibrous aggregate block which is uniform and low in bulk density is difficult to produce.
Further, across the portions of the internal surface of the mold 700, with which the fibers come into contact, melted fibers (fibers which have the relatively low melting point and act as bonding agent) spread flat. As a result, a porous skin, which is smaller in porosity than the internal portion of the multilayered fibrous material block 610, is formed in a manner to wrap the multilayered fibrous material block 610 along the internal surface of the mold 700. Depending upon the type of fibrous aggregate usage, the presence of this skin is undesirable, and therefore, a process for removing the skin becomes necessary, which is a problem in that the removal of the skin reduces yield relative to the amount of raw material.
The primary object of the present invention is to provide a method and an apparatus which are capable of forming a thicker fibrous aggregate which is low and uniform in bulk density, in particular, a method and an apparatus which are capable of forming such a fibrous aggregate even when the fibers in the multilayered fibrous material used for the formation of a fibrous aggregate are the same in properties, are not very different in melting point, and/or are relatively low in melting point.
A fibrous aggregate forming method in accordance with the present invention for accomplishing the above described objects is a method for thermally processing fibrous material to form a fibrous aggregate, and comprises: a heating process in which heated air is blown upward through the fibrous material from below the fibrous material to melt at least a portion of each fiber of the predetermined group of fibers in the fibrous material, while keeping the fibrous material afloat and in the same state as it was prior to the blowing of the heated air; a compressing process in which the heated fibrous material is compressed to a desired thickness from the top and bottom sides; and a cooling process in which the fibrous material is cooled to solidify the melted portion of each fiber, so that the fibers are firmly welded to each other at their intersections.
A fibrous aggregate forming apparatus in accordance with the present invention is an apparatus for thermally processing a fibrous material to form a fibrous aggregate, and comprises: a supporting means on which the aforementioned fibrous material is mounted; a heated air flow generating means for blowing the heated air for the heating process for melting at least a portion of each fiber, upward from below the fibrous material to lift and keep afloat the fibrous material from the supporting means; a compressing means for compressing the fibrous material toward the supporting means; and an attitude controlling means for controlling the attitude of the fibrous material kept afloat by the heated air.
According to one of the aspects of the present invention, while the fibrous material is thermally processed, it is lifted and kept afloat by blowing heated air upward at the fibrous material from directly below the fibrous material, and the attitude of the fibrous material kept afloat is regulated. As a result, the effect of the gravity which affects formation of fibrous aggregate is eliminated, and therefore, relatively thick fibrous aggregate which is relatively low in bulk density can be easily obtained.
In particular, a ventilatory sheet is placed in contact with the top and bottom surfaces of the fibrous material, and therefore, the surface pattern of the members used to compress the fibrous material is not imprinted onto the skin layer, or the top layer, of the fibrous material.
These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.